The present invention relates to a water heater comprising a plate heat exchanger and a storage container for heated water.
Hot water, in particular sanitary water, is often obtained by passing cold water through a plate heat exchanger to which a hot fluid is supplied in a secondary circuit. For household use the temperature at the tap should be kept constant e.g. between 55 and 60xc2x0 C. In many applications it is desired to heat the water directly in accordance with the flow needed so as to avoid unnecessary storing. However, some storage is unavoidable viz. the amount of water in the plate heat exchanger and the tubing to the taps. The use of plate heat exchangers makes it possible to obtain an efficient heat exchange and to supply a great mass flow of heated water with a minimum of storage volume. A problem inherent in the system is that if hot water has been tapped for some time followed by a short interval without flow, a new hot water flow will cause the temperature of the first amount of water to become substantially higher than desired. Hot water supplied at a temperature above 60xc2x0 C. may be dangerous if used e.g. for washing babies. The high water temperature is due to the fact that the fluid heating the water in the plate heat exchanger must have a temperature 10-20xc2x0 C. higher than the desired temperature of the water to be tapped. When the flow through the heat exchanger is stopped the sanitary water present in the exchanger will be heated to the temperature of the heating fluid in the exchanger. For reasons of safety a storage container for the hot water could be provided between the heat exchanger and the taps. A long tubing between the exchanger and the taps may constitute such container. However, such tubing may not be practical to provide and is certainly not desired as the first amount of water delivered to a tap after no use of hot water during a long period will be rather cold.
Therefore, it is desired to provide a water heater which has a small volume, but still prevents peak temperatures of the hot water when starting tapping after a short stop interval following a longer tapping period. Besides a small volume the water heater should also have small outer dimensions. In most cases the use of spherically shaped containers is impossible and other shapes may be deformed by the comparatively high water pressures which may occur. The use of heavy walled containers is prohibited for cost reasons.
A water heater comprising a plate heat exchanger and a storage container for heated water, the said storage container being provided with an outer limiting wall, an exit opening for delivery of the heated water and reinforcing means adapted to interconnect opposite parts of the wall for force transmitting in three directions perpendicular to each other is according to the invention characterized in that said reinforcing means in the storage container are stacked plates provided with ridges and depressions and are interconnected by brazing, soldering, welding or gluing, the said plates being provided with openings forming channels through which heated water may flow.
Such reinforcing means make it possible to design the container with extremely thin walls, and still allow high internal pressures without deformations. The container is not bound to be of spherical or cylindrical shape.
Preferably the container may be designed with the same outer shape and size as that of the heat exchanger in two directions perpendicular to each otherxe2x80x94making it possible to mount it e.g. as a continuation of the plate heat exchanger.
The container could be designed as a conventional two-circuit liquid to liquid plate heat exchanger in which only one circuit is used. However, both circuit passages could be used advantageously, if at least one plate therein is shaped to provide a connection between the two circuits.
Most preferably the container could be designed so as to form an integral part of the plate heat exchanger supplying the heated water to be stored in the container.